I. Field of the Invention
The invention relates to fluid actuated motors, more specifically to rodless fluid actuated motors and, in particular, to oval rodless fluid actuated cylinders.
II. Description of the Prior Art
Rodless cylindrical piston fluid actuated motors are, generally speaking, known in the art. Several different configurations have been produced and are commercially available. For example, one manufacturer offers a rodless cylinder including a cylinder tube having an internal circular bore extending longitudinally through the cylinder tube. The cylinder tube is closed at the ends by first and second end caps. The internal longitudinal circular bore communicates with the exterior of the cylinder tube through a longitudinal slot through the wall of the cylinder tube. The internal chamber formed by the circular bore is sealed by a lip seal at each end of the circular piston disposed therein and flexible zip-lock-configured sealing strips. The two spaced cylindrical piston halves are joined by a yoke, and a carriage is carried externally of the cylinder tube while being connected to the yoke.
Another manufacturer provides a cylinder barrel which has a slit along its entire length. Force is transmitted by means of a lug screwed to the piston and projecting through the slit. A thin steel band covers the full length of the slit from the inside and provides sealing. The steel band runs under the lug between the two piston rubber seals. Another steel band covers the slit from the outside and prevents dirt from coming in. The two sealing bands are kept in place by permanent magnets located along the slit. The cylinders have square end covers retained by four screws. The nuts are recessed in the outer end cover surface and extend so that the outer part of the nut thread is used for the mounting bolts retaining the cylinder mounting to the end cover. Each end cover has an air connection port and a throttle screw for adjusting the required cushioning capacity. The piston is provided with plastic support rings and rubber seals at each end. The piston lug is designed as a double yoke to allow the two sealing bands to run through. The section of the lug running in the cylinder slit is fitted with plastic slide strips to absorb lateral forces. The sealing bands are made of hardened stainless steel. Piston seals and O-rings are made of oil resistant rubber. Cushioning results from the restriction of the exhaust air flow when the spigot enters the recess in the piston. The setting of the throttle screw determines the pressure rise in the trapped air, i.e. the back pressure which cushions the piston. In order that the piston may start its return stroke under full power, the cushion seal is designed to allow free passage of air for filling the cylinder chamber. Both of these configurations require inner and outer bands which connect with one another to effect sealing of the inner chamber. In the first manufacturer's configuration, the drive tongue that connects the yoke/piston with the carriage passes through the tube slot. The tube is sealed by a lip seal at each of the pistons and by flexible "zip-lock" configured plastic seals. As the piston moves, the flexible seals are separated by the yoke along the unpressurized area between the piston seals. The seals are then reconnected to maintain a seal along pressurized areas. In the second manufacturer's configuration, the two seals are separated by the yoke along the unpressurized area between the piston seals. The inner band engages the interior surface of the circular bore, while the outer band engages the exterior of the cylinder barrel, which supports longitudinal seals on the exterior surface of the cylinder barrel that come into contact with the outer band on either side of the longitudinal slot.
A third manufacturer provides a rodless cylinder with a pneumatic brake. The cylinder features a dual chamber tube with each chamber being isolated from the other. The lower (pressurized) chamber houses the power piston. Compressed air enters the lower chamber to push the power piston. The power piston is attached to the (non-pressurized) upper carriage by a high tensile stainless steel band which actually pulls the load. The high tensile stainless steel band is attached to the outer end faces of the internal power piston and communicates with the upper carriage by passing through the end caps being guided by pulleys located in each end cap prior to attachment to the respective outer end faces of the carriage. The power band is sealed at both ends of the (pressurized) lower chamber to prevent leakage. The carriage assembly includes a pneumatically actuated mechanical brake to stop and hold the moving load. Actuating a three-way normally closed valve to direct air into the brake assembly causes the brake boot and brake pads to expand and firmly grip the inner wall of the top chamber. The three-way brake valve can be signaled by a timer, electric lead switches or mechanical microswitches which can be mounted along the side of the cylinder.